The present invention is directed to a method and apparatus for rotating digital images. In particular, the present invention is directed to a digital framestore architecture in which digital image information is stored in a first orientation and retrieved in a second orientation.
Digital imaging technology, including still and motion video cameras, document scanners and digital printers, provides the unique opportunity of being able to manipulate and enhance a digitally generated image to reproduce the image in any desired format. For example, the digital image data can be manipulated so that portions of the originally image are cropped--i.e. blocked from being reproduced--from the reproduced image, the size of the reproduced image can be altered, or the reproduced image can be rotated from the orientation of the original image. In addition, image enhancement techniques can be employed to improve the overall aesthetics of the reproduced image.
Image rotation is particularly useful when attempting to display images captured with a still video camera on a video monitor. Many times the operator of the camera will rotate the camera from the normal viewing position, usually either a positive 90 degrees or a negative 90 degrees, in order to record an image that cannot be properly framed in the normal viewing position. In such a case, the recorded image must be rotated before it is displayed on a video monitor, as a normal reproduction of the recorded image will result in the reproduced image being rotated 90 degrees with respect to the normal viewing position of the monitor.
Different methods of rotating a digital image have been proposed. Many utilize techniques that store image data in a memory or framestore, read the stored image data, and manipulate the data to represent a rotated image. U.S. Pat. No. 4,837,845 issued to Pruett et al. on Jun. 6, 1989, for example, discloses a method of transposing image data to accomplish image rotation and also notes a number of different references which discuss image rotation. The method disclosed in this patent, however, is accomplished through software routines and requires processing time to accomplish the rotation function. Image rotation utilizing hardware devices have also been proposed as shown in U.S. Pat. No. 4,636,783 issued to Omachi on Jan. 13, 1987, which utilizes shift-registers to accomplish the rotation function.
One of the primary disadvantages of many conventional rotation techniques that read image data from a framestore and then manipulate the data is the inability to operate in real time at the required pixel rates. For example, the international sampling rate standard (CCIR) is 13.5 MHz, which equates to 74 nsec/pixel, does not provide sufficient time to practically perform the image data manipulation in real time using either hardware or software techniques. Thus, it would be desirable to provide a direct addressing scheme that would read the image data from the framestore in the order required to generate a rotated image.
Conventional framestore devices, while capable of direct addressing in real time for normally oriented images, are not capable of providing direct addressing to provide rotated image data in real time. The primary problem with conventional framestores, as will be discussed in greater detail below, is that the addressing of the memory devices in the framestore for retrieval of rotated image data requires a single memory device to be addressed more than once during a single read cycle which, of course, cannot be accomplished. Accordingly, it is an object of the present invention to provide a framestore architecture that permits direct addressing of digital image data in order to generate rotated image data without requiring multiple addressing of a memory device within a single read cycle. It is a further object of the invention to provide a framestore architecture that provides direct addressing at standard video sampling rates.